1. Field of the Invention
The present invention relates to a path setting method in a network segmented into a plurality of areas and to a communication device employed in the network.
2. Description of the Related Art
There is an MPLS (Multi-Protocol Label Switching) technology as a technology enabling a packet to be transferred at a high speed. In the MPLS, unlike the conventional IP (Internet Protocol) routing, a packet is transferred based on a label attached to the packet.
Further, GMPLS (Generalized Multi-Protocol Label Switching) is given as a technology in which a concept of the MPLS is extended to and developed in a network (e.g., optical network) other than an IP network. In the GMPLS, for example, a concept of the label is applied to a wavelength of an optical signal in a WDM (Wavelength Division Multiplexing) network, and a transfer route is determined based on this wavelength.
The network employing the MPLS or the GMPLS is managed in physical or logical separation into a transmission network (which will hereinafter be referred to as a data plane) for transferring real data and a control network (which will hereinafter be referred to as a control plane) for conducting transfer control etc. of the real data. FIG. 15 is a diagram showing concepts of the data plane and the control plane in an MPLS/GMPLS network. As shown in FIG. 15, each of communication devices configuring the MPLS/GMPLS network has a control function (Nxx) and a transmission function (Dxx), and the MPLS/GMPLS network is configured by a control plane 1001 defined as a network to which the control functions (Nxx) of the communication devices are respectively connected and by a data plane 1002 defined as a network to which the transmission functions (Dxx) are respectively connected. For instance, a control function N11 and a transmission function D11 operate on one single communication device (1003 in FIG. 15).
On the control plane in this type of MPLS/GMPLS network, a control message based on three protocols that will be shown as below is exchanged. With this exchange of the message, the transfer control etc. of the real data flowing on the data plane is actualized.
A first protocol is a routing (which will hereinafter termed control plane routing) protocol used for each node to grasp a network topology of the control plane. Each of the nodes generates an LSA (Link State Advertisement) about a link between neighboring nodes on the control plane, and transmits the LSA to all the neighboring nodes on the control plane by use of the control plane routing protocol. The LSA contains items of information such as a self-node ID, an interface ID of the self-node, a neighboring node ID, an interface ID of the neighboring node and a cost on a link-by-link basis. The node receiving the LSA, if the information thereof is not-yet-received information, transfers this LSA to another neighboring node on the control plane. Given as this type of control plane routing protocol are OSPF (Open Shortest Path First) (refer to the following Non-Patent document 1), IS-IS (Intermediate System—Intermediate System) and so on.
A second protocol is a routing (which will hereinafter be called a data plane routing) protocol used for each node to grasp a network topology of the data plane. Each node generates an Opaque LSA (which will hereinafter be abbreviated to O-LSA) (refer to the following Non-Patent document 2) about a link between the neighboring nodes on the data plane, and transmits the O-LSA to all the neighboring nodes on the control plane. The O-LSA contains, in addition to the items of information contained in the LSA, items of information such as a bandwidth of the link and attribute values etc. of a data type of the link. The node receiving the O-LSA, if the information thereof is not-yet-received information, transfers the O-LSA to another neighboring node on the control plane. The data plane routing protocol is exemplified such as OSPF-TE (OSPF-Traffic Engineering) (refer to the following Non-Patent documents 3 and 4) and IS-IS TE.
FIG. 16 is a diagram showing concepts of the control plane routing and the data plane routing described above. As shown in FIG. 16, each node broadcasts the self-generated LSA and O-LSA to all the nodes on the control plane, and, when receiving the LSA and O-LSA from other nodes, transfers the LSA and O-LSA to another neighboring node.
A third protocol is a signaling protocol for setting a path in each of the nodes on the data plane. When setting the path, a path establishing request message and a path establishing response message are exchanged between the respective nodes on the path to be established. When releasing the path, a path delete request message and a path delete response message are exchanged between the respective path-already-set nodes. This type of signaling protocol is exemplified such as RSVP-TE (resource ReSerVation Protocol-Traffic Engineering) (refer to the following Non-Patent documents 5 and 6) and CR-LDP (Constraint-based Label Distribution Protocol).
The path establishing request message described above contains a path identifier, path attribute values (a bandwidth, a priority level, etc.), route information and so on. Any one of node information about all the nodes included in the path from an originating node to a terminating node, node information about some nodes included in the path from the originating node to the terminating node, and node information about only the terminating node, is set as the route information. A method of designating all the nodes included in the path in the path establishing request message is called full-strict designation.
Further, it is also possible to designate some nodes, thorough which the path goes, in the path establishing request message or to designate only the terminating node, in which case strict designation or loose designation is used. The strict designation is used in such a case that the strict-designated node is determined as a next downstream node on the should-be-established path, while the loose designation is used in a case where the path may go through other nodes on a route down to the loose-designated node.
A path establishing operation based on this type of signaling protocol will be explained with reference to FIG. 17. FIG. 17 is a diagram showing an operation of the path establishing signaling of a path from an originating node D11 to a terminating node D22. A node N11 on the control plane, which corresponds to the originating node D11 (the node D11 and the node N11 exist in the same communication device) generates a path establishing request message ([Path] shown in FIG. 17). At this time, the originating node N11 sets, in the route information of this path establishing request message, the node information of only the node N22 as the terminating node, or the node information of all the via-nodes (N11, N12, N14, N16, N18, N20, N22) on the path, or the node information of some via-nodes (e.g., N14, M18, N22) on the path. This route information is obtained by performing a route calculation (routing algorithm) based on, for example, the information in the O-LSA, i.e., the network topology information of the data plane, or is set through manual inputting by a network administrator who requests the path to be established.
The originating node N11 determines based on the generated route information that a neighboring via-node on the path is a node D12. Then, the originating node N11, when judging from the information in the O-LSAs collected by using the data plane protocol that a link between the neighboring node D12 and the self-node can be established, sets the path in the node D11, thereby establishing the path. Then, the originating node N11 transmits the path establishing request message to the node N12 on the control plane, which corresponds to the neighboring node D12.
Thereafter, the relay nodes (N12, N14, N16, N18, N20) each receiving the path establishing request message set the path in corresponding transmission nodes (D12, D14, D16, D18, D20). When establishing the path, each of the relay nodes transfers the path establishing request message to a next downstream node in accordance with the route information stored in the path establishing request message. If the route information in the path establishing request message is the loose designation, the relay node computes a route from the network topology of the data plane and determines the downstream nodes. At this time, the relay node adds a result of the computation to the route information in the path establishing request message as the necessity may arise.
The terminating node N22, upon receiving the path establishing request message, effects the path setting in the transmission node D22 within the self-device, thereby establishing the path. Then, the terminating node N22, for notifying the originating node N11 that the path is completely established, sends a path establishing response message back to the originating node N11 in a way that traces back the route along which the path establishing request message has been transferred. When this path establishing response message reaches the originating node N11, the path establishing signaling is finished.
It should be noted that a path establishing signaling delete procedure likewise exists. Further, the discussion given above has exemplified the case, wherein the path setting in each transmission node (Dxx) is done when receiving the path establishing request message and so on, however, there might be a case of effecting the path setting when receiving the path establishing response message and so forth.
Moreover, the path establishing signaling has a function of establishing, if a link not satisfying a request is detected in the midway node in the process of the path establishing procedure and when the midway node searches for an alternate route different from the designated route, the path along this alternate route. This function is called crankback (refer to the following Non-Patent document 7). Herein, the crankback will be explained with reference to FIG. 18. FIG. 18 is a diagram showing a crankback operation of the path establishing signaling. FIG. 18 exemplifies a case where there is a path establishing request of a path from an originating node N1 to a terminating node N6 on the control plane.
The originating node N1 sets N1->N2->N3->N4->N5->N6 as a route to the terminating node N6, and sends the path establishing request message to the neighboring node N2 ((1) PATH). The relay node N4 tries to establish the path between the self-node and the node N5 defined as a downstream node on the route in accordance with the route information in this path establishing request message, however, if unable to establish the path due to an error such as a lack of bandwidth, the node N4 sends a path establishing error message ((5) PATHERR in FIG. 18) stored with error link information back to the upstream node N3. The path establishing error message is transferred up to the node N2 having the crankback function.
The node N2 having the crankback function, when receiving the path establishing error message, deletes the error link from the network topology of the data plane, and performs the route calculation, thus searching for an alternate route ((7) in FIG. 18). The example n FIG. 18 is that the route via the node N7 is searched for, and the path establishing request message containing the route information of this searched route is sent toward the node N7. Note that the node N2, if unable to search for the alternate route through the route calculation, sends, it follows, the path establishing error message stored with information about the error point toward the upstream node on the path.
The Non-Patent document 1 is ““OSPF Version 2”, Network Working Group Request for Comments (RFC) 2328, April 1998.”
The Non-Patent document 2 is ““The OSPF Opaque LSA Option”, Network Working Group Request for Comments (RFC) 2370, July 1998.”
The Non-Patent document 3 is ““Traffic Engineering (TE) Extensions to OSPF Version 2”, Network Working Group Request for Comments (RFC) 3630, September 2003.”
The Non-Patent document 4 is ““OSPF Extensions in Support of Generalized Multi-Protocol Label Switching”, Network Working Group Internet Draft, October 2003.”
The Non-Patent document 5 is ““RSVP-TE: Extensions to RSVP for LSP Tunnels”, Network Working Group Request for Comments (RFC) 3209, December 2001.”
The Non-Patent document 6 is ““Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions”, Network Working Group Request for Comments (RFC) 3473, January 2003.”
The Non-Patent document 7 is ““Crankback Signaling Extensions for MPLS and GMPLS RSVP-TE”, Network Working Group Internet Draft, May 2005.”
The MPLS/GMPLS network described above has, however, a problem that each node must retain the information about all other nodes on the control plane and on the data plane, and consequently a database of each node is hypertrophied. Further, another problem is that a quantity of the information exchanged within the network increases.
Such being the case, a technique of managing the network in a way that segments the network into a plurality of areas, is adopted. FIG. 19 is a diagram illustrating the MPLS/GMPLS network in the case of its being segmented into the plurality of areas. An example in FIG. 19 shows that the network is segmented into an area 1, an area 2 and an area 0 serving as a backbone area for the areas 1 and 2. Then, on the control plane, the nodes N14 and N15 are provided at a boundary between the area 1 and the area 0, while the nodes N18 and N19 are provided at a boundary between the area 0 and the area 2. On the data plane, the boundary nodes are the transmission nodes (D14, D15, D18, D19) corresponding to the boundary nodes on the control plane.
Herein, a description of how the control plane routing, the data plane routing and the signaling explained earlier operate on the network thus segmented into the plurality of areas, will hereinafter be made. In the following discussion, the OSPF is exemplified as the control plane routing, the OSPF-TE is exemplified as the data plane routing, and the RSVP-TE is exemplified as the signaling protocol.
To begin with, the operation of the control plane routing will be explained with reference to FIGS. 20 and 21. FIG. 20 is a diagram showing the control plane routing in the area 0 serving as the backbone area. FIG. 21 is a diagram showing the control plane routing in the area 1. The OSPF is an IP routing protocol and has a function of summarizing a network topology of each individual area and notifying the other areas of the summarized topology in order to actualize transferring IP packets between the plurality of areas.
With this operation, in the area 0, the boundary nodes N14 and N15 respectively generate summary LSAs about links between the nodes N11, N12, N13 in the area 1 and the boundary nodes, and send the summary LSAs to other nodes in the area 0. The summary LSA is generated to contain information such as a link cost of a link on the assumption that a node existing in a different area but not neighbored is virtually connected. For example, the boundary node N14 is, though not neighbored to the node N11, assumed to be neighbored thereto and generates the summary LSA. Similarly, the boundary nodes N18 and N19 generate the summary LSAs with respect to the nodes N20, N21 and N22 in the area 2, and send the summary LSAs to other nodes within the area 0.
In the area 1, as shown in FIG. 21, the boundary nodes N14 and N15 generate the summary LSAs about the links between the respective nodes belonging to the area 0 and the area 2 and the boundary nodes, and then send the summary LSAs to other nodes in the area 1. Note that the nodes N11, N12 and N13 each defined as none of the boundary node generate the LSAs and send the LSAs to other nodes. In the area 2, as in the case of the area 1, the nodes N18 and N19 defined as the boundary nodes generate the summary LSAs.
Next, an operation of the data plane routing will be explained with reference to FIGS. 22 and 23. FIG. 22 is a diagram showing the data plane routing in the area 0 defined as the backbone area. FIG. 23 is a diagram showing the data plane routing in the area 1. As shown in FIGS. 22 and 23, the OSPF-TE has no function of notifying of the link information over the area, and hence each node is unable to know the link information etc. on the data plane with respect to other nodes outside the area. This is because the IP routing protocol handles only the cost and the topology about the respective links, and, by contrast, the data plane routing protocol such as the OSPF-TE comes to handle a multiplicity of parameters such as link bandwidth information and a type of fault recovery function, and outline information is hard to be created.
Thus, in the conventional MPLS/GMPLS network, in the case of segmenting the network into the plurality of areas, as to the data plane, the link information in the other areas can not be exchanged, and consequently a problem arises, wherein a path to the node in another area can not be automatically established.
Then, to solve this problem, there has hitherto been adopted such a technique that a network administrator, if needed to set the path over the area, fixedly sets a should-be-through boundary node. This method has, however, a problem that at-once flexibility can not be given to a case where a predetermined path can not be set due to deficiency of the link bandwidth, a link fault, etc.